Combining waveforms to treat chronic pain without causing paresthesia

ABSTRACT

A neuromodulation system and method of providing therapy to a patient. A plurality of individual electrical pulse trains is generated at a respective plurality of individual pulse rates. The plurality of individual electrical pulse trains are concurrently respectively from a plurality of electrodes to a common electrode via tissue of the patient, thereby creating a combined electrical pulse train having an average pulse rate equal to or greater than 1 KHz.

RELATED APPLICATION DATA

The present application is a continuation of U.S. application Ser. No.13/931,090, filed Jun. 28, 2013, which claims the benefit under 35U.S.C. §119 to U.S. provisional patent application Ser. No. 61/666,833,filed Jun. 30, 2012. The foregoing applications are hereby incorporatedby reference into the present application in their entirety.

FIELD OF THE INVENTION

The present invention relates to tissue modulation systems, and moreparticularly, to a system and method for delivering high-frequencyneuromodulation electrical energy to provide therapy.

BACKGROUND OF THE INVENTION

Implantable neuromodulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of spinal modulation has begun to expand to additionalapplications, such as angina pectoris and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory Parkinson's Disease, and DBS hasalso recently been applied in additional areas, such as essential tremorand epilepsy. Further, in recent investigations, Peripheral NerveStimulation (PNS) systems have demonstrated efficacy in the treatment ofchronic pain syndromes and incontinence, and a number of additionalapplications are currently under investigation. Furthermore, FunctionalElectrical Stimulation (FES) systems such as the Freehand system byNeuroControl (Cleveland, Ohio) have been applied to restore somefunctionality to paralyzed extremities in spinal cord injury patients.

Each of these implantable neuromodulation systems typically includes oneor more electrode carrying modulation leads, which are implanted at thedesired stimulation site, and a neuromodulation device implantedremotely from the stimulation site, but coupled either directly to theneuromodulation lead(s) or indirectly to the neuromodulation lead(s) viaa lead extension. Thus, electrical pulses can be delivered from theneuromodulation device to the electrode(s) to activate a volume oftissue in accordance with a set of modulation parameters and provide thedesired efficacious therapy to the patient. In particular, electricalenergy conveyed between at least one cathodic electrode and at least oneanodic electrode creates an electrical field, which when strong enough,depolarizes (or “stimulates”) the neurons beyond a threshold level,thereby inducing the firing of action potentials (APs) that propagatealong the neural fibers. A typical modulation parameter set may includethe electrodes that are sourcing (anodes) or returning (cathodes) themodulating current at any given time, as well as the amplitude,duration, and rate of the stimulation pulses.

The neuromodulation system may further comprise a handheld patientprogrammer to remotely instruct the neuromodulation device to generateelectrical stimulation pulses in accordance with selected modulationparameters. The handheld programmer in the form of a remote control (RC)may, itself, be programmed by a clinician, for example, by using aclinician's programmer (CP), which typically includes a general purposecomputer, such as a laptop, with a programming software packageinstalled thereon.

Of course, neuromodulation devices are active devices requiring energyfor operation, and thus, the neuromodulation system may oftentimesincludes an external charger to recharge a neuromodulation device, sothat a surgical procedure to replace a power depleted neuromodulationdevice can be avoided. To wirelessly convey energy between the externalcharger and the implanted neuromodulation device, the charger typicallyincludes an alternating current (AC) charging coil that supplies energyto a similar charging coil located in or on the neuromodulation device.The energy received by the charging coil located on the neuromodulationdevice can then be used to directly power the electronic componentrycontained within the neuromodulation device, or can be stored in arechargeable battery within the neuromodulation device, which can thenbe used to power the electronic componentry on-demand.

Typically, the therapeutic effect for any given neuromodulationapplication may be optimized by adjusting the modulation parameters.Often, these therapeutic effects are correlated to the diameter of thenerve fibers that innervate the volume of tissue to be modulated. Forexample, in SCS, activation (i.e., recruitment) of large diametersensory fibers is believed to reduce/block transmission of smallerdiameter pain fibers via interneuronal interaction in the dorsal horn ofthe spinal cord. Activation of large sensory fibers also typicallycreates a sensation known as paresthesia that can be characterized as analternative sensation that replaces the pain signals sensed by thepatient.

Although alternative or artifactual sensations are usually toleratedrelative to the sensation of pain, patients sometimes report thesesensations to be uncomfortable, and therefore, they can be considered anadverse side-effect to neuromodulation therapy in some cases. It hasbeen shown that high-frequency pulsed electrical energy can be effectivein providing neuromodulation therapy for chronic pain without causingparesthesia. In contrast to conventional neuromodulation therapies,which employ low- to mid-frequencies to provide a one-to-onecorrespondence between the generation of an AP and each electricalpulse, high frequency modulation (e.g., 1 KHz-50 KHz) can be employed toblock naturally occurring APs within neural fibers or otherwise disruptthe APs within the neural fibers. Although high-frequency modulationtherapies have shown good efficacy in early studies, it would bedesirable to provide high-frequency modulation therapy using alreadyexisting lower frequency sources.

There, thus, remains a need to decrease the energy requirements forhigh-frequency neuromodulation therapy.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present inventions, aneuromodulation system comprises a plurality of electrical terminalsconfigured for being coupled to a respective plurality of electrodes,and modulation output circuitry configured for respectively generating aplurality of individual electrical pulse trains (which may includemonophasic pulses or multiphasic pulses) at a plurality of pulse rates.In one embodiment, the modulation output circuitry comprises a singleelectrical source for generating the plurality of electrical pulsetrains. In another embodiment, the modulation output circuitry comprisesa plurality of electrical sources for respectively generating theplurality of electrical pulse trains. The modulation output circuitrymay be configured for generating at least two of the plurality ofindividual electrical pulse trains in accordance with different valuesof a modulation parameter that comprises one of a pulse amplitude, pulseduration, and pulse shape. The neuromodulation system further comprisesa switching network coupled between the plurality of electricalterminals and the modulation output circuitry. At least two of theplurality of pulse rates may be identical to each other or may differfrom each other.

The neuromodulation system further comprises control circuitryconfigured for operating the switching network to concurrently conveythe plurality of electrical pulse trains respectively from a pluralityof electrical terminals to a common electrical terminal, therebycreating a combined electrical pulse train having an average pulse rateequal to or greater than 1 KHz. The average pulse rate may be equal tothe sum of the plurality of pulse rates. In one embodiment, the averagepulse rate is less than 50 KHz. The combined electrical pulse train atthe common electrical terminal may be anodic.

The control circuitry may be configured for operating the switchingnetwork without arbitration, such that the pulses of each respectiveindividual electrical pulse train are uniformly spaced from each other.Or the control circuitry maybe configured for operating the switchingnetwork with arbitration, such that the pulses of at least one of theplurality of individual electrical pulse trains are variably spaced fromeach other in a manner that limits the time intervals between the pulsesof the combined electrical pulse train to a minimum time interval. Inone embodiment, the control circuitry is configured for instructing themodulation output circuitry to generate each of the individualelectrical pulse trains in accordance with a cyclically varying set ofmodulation parameters. In another embodiment, the control circuitry isconfigured for instructing the modulation output circuitry to repeatedlygenerate the plurality of individual electrical pulse trains in abursting pattern.

In an optional embodiment, the modulation output circuitry is furtherconfigured for generating another plurality of individual electricalpulse trains at another respective plurality of pulse rates, and thecontrol circuitry is further configured for operating the switchingnetwork to concurrently convey the other plurality of individualelectrical pulse trains respectively from another plurality ofelectrical terminals to another common electrical terminal, therebycreating another combined electrical pulse train having another averagepulse rate greater than 1 KHz.

In another optional embodiment, the neuromodulation system furthercomprises a user interface configured for receiving an input from a userspecifying the electrode corresponding to the common electricalterminal, in which case, the control circuitry may be configured forselecting the common electrical terminal in response to the input fromthe user specifying the electrode corresponding to the common electricalterminal. The control circuitry may also be configured for automaticallyselecting the plurality of electrical terminals in response to the inputfrom the user specifying the electrode corresponding to the commonelectrical terminal.

In another embodiment, the user interface is further configured forreceiving an input from the user specifying electrodes corresponding tothe plurality of electrical terminals, in which case, the controlcircuitry may be configured for selecting the plurality of electricalterminals in response to the user input specifying the electrodescorresponding to the plurality of electrical terminals. In still anotherembodiment, the user interface is further configured for receiving aninput from the user specifying an electrode corresponding to anelectrical terminal, in which case, the control circuitry may beconfigured for selecting the plurality of electrical terminals that doesnot include the electrical terminal in response to the user inputspecifying the electrode corresponding to the electrical terminal.

In accordance with a second aspect of the present inventions, a methodof providing therapy to a patient is provided. The method comprisesgenerating a plurality of electrical pulse trains (which may includemonophasic pulses or multiphasic pulses) at a respective plurality ofpulse rates. At least two of the plurality of individual electricalpulse trains may be generated in accordance with different values of amodulation parameter that comprises one of a pulse amplitude, pulseduration, and pulse shape. At least one pulse in each of the pluralityof individual electrical pulse trains is multiphasic. At least two ofthe plurality of pulse rates may be identical to each other or maydiffer from each other.

The method further comprises concurrently conveying the plurality ofelectrical pulse trains respectively from a plurality of electrodes to acommon electrode via tissue of the patient, thereby creating a combinedelectrical pulse train having an average pulse rate equal to or greaterthan 1 KHz. The average pulse rate may be equal to the sum of theplurality of pulse rates. In one method, the average pulse rate is lessthan 50 KHz. In another method, the tissue adjacent the common electrodeis therapeutically modulated by the combined electrical pulse train toprovide the therapy, whereas the tissue adjacent the plurality ofelectrodes is not therapeutically modulated by the plurality ofelectrical pulse trains.

In one method, the conveyance of the plurality of individual electricalpulse trains is not arbitrated, such that the pulses of each respectiveindividual electrical pulse trains are uniformly spaced from each other.In another method, the conveyance of the plurality of individualelectrical pulse trains is not arbitrated, such that the pulses of atleast one of the plurality of individual pulse trains are variablyspaced from each other in a manner that limits the time intervalsbetween the pulses of the combined electrical pulse train to a minimumtime interval. Each of the individual electrical pulse trains may begenerated in accordance with a cyclically varying set of modulationparameters and/or plurality of individual electrical pulse trains may berepeatedly generated in a bursting pattern.

An optional method further comprises generating another plurality ofindividual electrical pulse trains at another respective plurality ofpulse rates, and concurrently conveying the other plurality ofindividual electrical pulse trains respectively from another pluralityof electrodes to another common electrode, thereby creating anothercombined electrical pulse train having another an average pulse rategreater than any of the other plurality of pulse rates.

Another optional method further comprises receiving an input from a userspecifying the common electrode, and selecting the common electrode inresponse to the input from the user specifying the common electrode. Theoptional method may comprise automatically selecting the plurality ofelectrodes in response to the input from the user specifying the commonelectrode. Or the optional method may comprise receiving an input fromthe user specifying electrodes corresponding to the plurality ofelectrodes, and selecting the plurality of electrodes in response to theuser input specifying the plurality of electrodes. Another methodcomprises receiving an input from the user specifying an electrode, andselecting the plurality of electrodes that does not include theelectrode in response to the user input specifying the electrode.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of an embodiment of a spinal cord modulation (SCM)system arranged in accordance with the present inventions;

FIG. 2 is a profile view of an implantable pulse generator (IPG) used inthe SCS system of FIG. 1;

FIG. 3 is a plot of monophasic cathodic electrical stimulation energy;

FIG. 4a is a plot of biphasic electrical stimulation energy having acathodic stimulation pulse and an active charge recovery pulse;

FIG. 4b is a plot of biphasic electrical stimulation energy having acathodic stimulation pulse and a passive charge recovery pulse;

FIG. 5 is a plan view of the SCM system of FIG. 1 in use with a patient;

FIG. 6 is a schematic diagram showing one example of operating theimplantable pulse generator of FIG. 2 to convey electrical pulse trainsfrom a plurality of electrodes to a common electrode;

FIG. 7 is a timing diagram of one arrangement of electrical pulse trainsconveyed from a plurality of electrodes to a common electrode;

FIG. 8 is a timing diagram of another arrangement of electrical pulsetrains conveyed from a plurality of electrodes to a common electrode;

FIG. 9 is a schematic diagram showing another example of operating theimplantable pulse generator of FIG. 2 to convey electrical pulse trainsfrom a plurality of electrodes to two common electrodes;

FIG. 10 is a timing diagram of an arrangement of electrical pulse trainsconveyed from a plurality of electrodes to two common electrodes;

FIG. 11 is a schematic diagram showing another example of operating theimplantable pulse generator of FIG. 2 to convey electrical pulse trainsfrom a plurality of electrodes to a common electrode;

FIG. 12 is a schematic diagram showing another example of operating theimplantable pulse generator of FIG. 2 to convey electrical pulse trainsfrom a plurality of electrodes to a common electrode;

FIG. 13 is a timing diagram of an arrangement of electrical pulse trainsconveyed from a plurality of electrodes to a common electrode;

FIG. 14 is a timing diagram of an arrangement of electrical pulse trainsconveyed from a plurality of electrodes to a common electrode withoutusing arbitration;

FIG. 15 is a timing diagram of an arrangement of electrical pulse trainsconveyed from a plurality of electrodes to a common electrode using onearbitration technique;

FIG. 16 is a timing diagram of an arrangement of electrical pulse trainsconveyed from a plurality of electrodes to a common electrode usinganother arbitration technique; and

FIG. 17 is a block diagram of the internal components of the IPG of FIG.2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord modulation (SCM)system. However, it is to be understood that the while the inventionlends itself well to applications in SCM, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neural stimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Turning first to FIG. 1, an exemplary Spinal Cord Modulation (SCM)system 10 generally includes one or more (in this case, two) implantablemodulation leads 12, an implantable pulse source (IPG) 14, an externalremote controller RC 16, a clinician's programmer (CP) 18, an ExternalTrial Modulator (ETM) 20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the neuromodulation leads 12, which carry a pluralityof electrodes 26 arranged in an array. In the illustrated embodiment,the neuromodulation leads 12 are percutaneous leads, and to this end,the electrodes 26 are arranged in-line along the neuromodulation leads12. In alternative embodiments, the electrodes 26 may be arranged in atwo-dimensional pattern on a single paddle lead. As will be described infurther detail below, the IPG 14 includes pulse generation circuitrythat delivers electrical stimulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of modulationparameters.

The ETM 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the neuromodulation leads 12. TheETM 20, which has similar pulse generation circuitry as that of the IPG14, also delivers electrical modulation energy in the form of a pulsedelectrical waveform to the electrode array 26 in accordance with a setof modulation parameters. The major difference between the ETM 20 andthe IPG 14 is that the ETM 20 is a non-implantable device that is usedon a trial basis after the neuromodulation leads 12 have been implantedand prior to implantation of the IPG 14, to test the responsiveness ofthe stimulation that is to be provided. Thus, any functions describedherein with respect to the IPG 14 can likewise be performed with respectto the ETM 20. Further details of an exemplary ETM are described in U.S.Pat. No. 6,895,280, which is expressly incorporated herein by reference.

The RC 16 may be used to telemetrically control the ETM 20 via abi-directional RF communications link 32. Once the IPG 14 and modulationleads 12 are implanted, the RC 16 may be used to telemetrically controlthe IPG 14 via a bi-directional RF communications link 34. Such controlallows the IPG 14 to be turned on or off and to be programmed withdifferent modulation parameter sets. The IPG 14 may also be operated tomodify the programmed modulation parameters to actively control thecharacteristics of the electrical modulation energy output by the IPG14.

The CP 18 provides clinician detailed modulation parameters forprogramming the IPG 14 in the operating room and in follow-up sessions.The CP 18 may perform this function by indirectly communicating with theIPG 14, through the RC 16, via an IR communications link 36.Alternatively, the CP 18 may directly communicate with the IPG 14 via anRF communications link (not shown). The clinician detailed modulationparameters provided by the CP 18 are also used to program the RC 16, sothat the modulation parameters can be subsequently modified by operationof the RC 16 in a stand-alone mode (i.e., without the assistance of theCP 18). The external charger 22 is a portable device used totranscutaneously charge the IPG 14 via an inductive link 38. Once theIPG 14 has been programmed, and its power source has been charged by theexternal charger 22 or otherwise replenished, the IPG 14 may function asprogrammed without the RC 16 or CP 18 being present. Details ofexemplary embodiments of external chargers are disclosed in U.S. Pat.No. 6,895,280, which has been previously incorporated herein byreference.

Referring to FIG. 2, the IPG 14 comprises an outer case 40 for housingthe electronic and other components (described in further detail below),and a connector 42 to which the proximal end of the neuromodulationleads 12 mate in a manner that electrically couples the electrodes 26 tothe internal electronics (described in further detail below) within theouter case 40. The outer case 40 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case40 may serve as an electrode.

In the embodiment illustrated in FIG. 2, the neuromodulation leads 12take the form of percutaneous leads on which the electrodes 26 (in thiscase, electrodes E1-E16) are disposed as ring electrodes. In theillustrated embodiment, two percutaneous leads 12(1) and 12(2) on whichelectrodes E1-E8 and E9-E16 are respectively disposed can be used withthe SCM system 10. The actual number and shape of leads and electrodeswill, of course, vary according to the intended application. Furtherdetails describing the construction and method of manufacturingpercutaneous stimulation leads are disclosed in U.S. patent applicationSer. No. 11/689,918, entitled “Lead Assembly and Method of Making Same,”and U.S. patent application Ser. No. 11/565,547, entitled “CylindricalMulti-Contact Electrode Lead for Neural Stimulation and Method of MakingSame,” the disclosures of which are expressly incorporated herein byreference.

As will be described in further detail below, the IPG 14 includes pulsegeneration circuitry that provides electrical modulation energy to theelectrodes 26 in accordance with a set of modulation parameters. Suchparameters may comprise electrode combinations, which define theelectrodes that are activated as anodes (positive), cathodes (negative),and turned off (zero), and electrical pulse parameters, which define thepulse amplitude (measured in milliamps or volts depending on whether theIPG 14 supplies constant current or constant voltage to the electrodes),pulse duration (measured in microseconds), pulse rate (measured inpulses per second), duty cycle (pulse duration divided by cycleduration), burst rate (measured as the modulation energy on duration Xand modulation energy off duration Y), and pulse shape.

With respect to the pulse patterns provided during operation of the SCMsystem 10, electrodes that are selected to transmit or receiveelectrical energy are referred to herein as “activated,” whileelectrodes that are not selected to transmit or receive electricalenergy are referred to herein as “non-activated.” Electrical energydelivery will occur between two (or more) electrodes, one of which maybe the IPG case 40, so that the electrical current has a path from theenergy source contained within the IPG case 40 to the tissue and a sinkpath from the tissue to the energy source contained within the case.Electrical energy may be transmitted to the tissue in a monopolar ormultipolar (e.g., bipolar, tripolar, etc.) fashion.

Monopolar delivery occurs when a selected one or more of the leadelectrodes 26 is activated along with the case 40 of the IPG 14, so thatelectrical energy is transmitted between the selected electrode 26 andcase 40. Monopolar delivery may also occur when one or more of the leadelectrodes 26 are activated along with a large group of lead electrodeslocated remotely from the one or more lead electrodes 26 so as to createa monopolar effect; that is, electrical energy is conveyed from the oneor more lead electrodes 26 in a relatively isotropic manner. Bipolardelivery occurs when two of the lead electrodes 26 are activated asanode and cathode, so that electrical energy is transmitted between theselected electrodes 26. Tripolar delivery occurs when three of the leadelectrodes 26 are activated, two as anodes and the remaining one as acathode, or two as cathodes and the remaining one as an anode.

The electrical energy may be delivered between a specified group ofelectrodes as monophasic electrical energy or multiphasic electricalenergy. As illustrated in FIG. 3, monophasic electrical energy includesa series of pulses that are either all negative (cathodic), oralternatively all positive (anodic). Multiphasic electrical energyincludes a series of pulses that alternate between positive andnegative.

For example, as illustrated in FIGS. 4a and 4b , multiphasic electricalenergy may include a series of biphasic pulses, with each biphasic pulseincluding a cathodic (negative) modulation pulse (during a first phase)and an anodic (positive) charge recovery pulse (during a second phase)that is generated after the modulation pulse to prevent direct currentcharge transfer through the tissue, thereby avoiding electrodedegradation and cell trauma. That is, charge is conveyed through theelectrode-tissue interface via current at an electrode during amodulation period (the length of the modulation pulse), and then pulledback off the electrode-tissue interface via an oppositely polarizedcurrent at the same electrode during a recharge period (the length ofthe charge recovery pulse).

The second phase may have an active charge recovery pulse (FIG. 4a ),wherein electrical current is actively conveyed through the electrodevia current or voltage sources, and a passive charge recovery pulse, orthe second phase may have a passive charge recovery pulse (FIG. 4b ),wherein electrical current is passively conveyed through the electrodevia redistribution of the charge flowing from coupling capacitancespresent in the circuit. Using active recharge, as opposed to passiverecharge, allows faster recharge, while avoiding the charge imbalancethat could otherwise occur. Another electrical pulse parameter in theform of an interphase can define the time period between the pulses ofthe biphasic pulse (measured in microseconds).

As shown in FIG. 5, the neuromodulation leads (or lead) 12 are implantedwithin the spinal column 46 of a patient 48. The preferred placement ofthe neuromodulation leads 12 is adjacent, i.e., resting near, or uponthe dura, adjacent to the spinal cord area to be stimulated. Theneuromodulation leads 12 will be located in a vertebral position thatdepends upon the location and distribution of the chronic pain. Forexample, if the chronic pain is in the lower back or legs, theneuromodulation leads 12 may be located in the mid- to low-thoracicregion (e.g., at the T9-12 vertebral levels). Due to the lack of spacenear the location where the electrode leads 12 exit the spinal column46, the IPG 14 is generally implanted in a surgically-made pocket eitherin the abdomen or above the buttocks. The IPG 14 may, of course, also beimplanted in other locations of the patient's body. The lead extensions24 facilitate locating the IPG 14 away from the exit point of theelectrode leads 12. As there shown, the CP 18 communicates with the IPG14 via the RC 16.

Significant to the present inventions, the SCM system 10 is capable ofconcurrently conveying a plurality of individual electrical pulse trainsrespectively from a plurality of electrodes to a common electrode,thereby creating a combined electrical pulse train at the commonelectrode. For the purposes of this specification, electrical pulsetrains are concurrently conveyed if any of their pulses overlap or areinterleaved relative to each other. The combined electrical pulse trainhas an average pulse rate that is greater than any of the pulse rates ofthe individual electrical pulse trains, and preferably, an average pulserate equal to the sum of the pulse rates. That is, the lower pulse ratesat the electrodes are summed together to create a higher pulse rate atthe common electrode. Significantly, this feature allows the SCM system10 to generate electrical pulse trains at a relatively high frequency(e.g., greater than 1 KHz) that may not be achievable by utilizing anindividual electrical pulse train.

In a preferred method, the individual pulse trains are respectivelyconveyed from the plurality of electrodes to the common electrode (orelectrodes) via tissue of the patient. Preferably, the tissue adjacentthe common electrode (or electrodes) is therapeutically modulated (e.g.,stimulated) by the combined electrical pulse train to provide thetherapy, and the tissue adjacent the plurality of electrodes is nottherapeutically modulated (e.g., not stimulated) by the plurality ofindividual electrical pulse trains.

For example, with reference to FIGS. 6 and 7, an electrical pulse trainhaving a pulse rate of 1 KHz can be conveyed from electrode E2 toelectrode E1, and an electrical pulse train having a pulse rate of 2 KHzcan be conveyed from electrode E3 to electrode E1. As a result, acombined electrical pulse train having an average pulse rate 3 KHz canbe created at electrode E1. As there shown, even though the timeintervals between the pulses of the combined electrical pulse train arenot uniform, the effective pulse rate of the combined electrical pulsetrain is 3 KHz. Although the individual electrical pulse trains conveyedfrom electrodes E2 and E3 are illustrated as being anodic andmonophasic, and therefore, the combined electrical pulse train atelectrode E1 is illustrated as being cathodic and monophasic, theindividual electrical pulse trains conveyed from electrodes E2 and E3may be cathodic and/or multiphasic, and therefore, the combinedelectrical pulse train at electrode E1 may be anodic and/or multiphasic.

Furthermore, although the individual pulse rates of the electrical pulsetrains conveyed from electrodes E2 and E3 are described as beingdifferent from each other, the individual pulse rates may be identicalto each other. For example, as shown in FIG. 8, an electrical pulsetrain having a pulse rate of 2 KHz can be conveyed from electrode E2 toelectrode E1, and an electrical pulse train having a pulse rate of 2 KHzcan be conveyed from electrode E3 to electrode E1. As a result, acombined electrical pulse train having an average pulse rate 4 KHz canbe created at electrode E1.

Although only a single common electrode is illustrated in FIGS. 7 and 8,electrical pulse trains can be conveyed to a plurality of commonelectrodes. For example, with reference to FIGS. 9 and 10, an electricalpulse train having a pulse rate of 1 KHz can be conveyed from electrodeE2 to electrode E1, an electrical pulse train having a pulse rate of 2KHz can be conveyed from electrode E3 to electrodes E1 and E4, and anelectrical pulse train having a pulse rate of 4 KHz can be conveyed fromelectrode E5 to electrode E4. As a result, a combined electrical pulsetrain having an average pulse rate 3 KHz can be created at electrode E1,and another combined electrical pulse train having an average pulse rateof 6 KHz can be created at electrode E4.

It should also be appreciated that the same electrical pulse trains canbe conveyed to more than one common electrode, or a single pulse traincan be conveyed from multiple electrodes. For example, as illustrated inFIG. 11, an electrical pulse train having a pulse rate of 1 KHz can beconveyed from electrode E2 to electrodes E1 and E4, and an electricalpulse train having a pulse rate of 2 KHz can be conveyed from electrodeE3 to electrodes E1 and E4. As a result, a combined electrical pulsetrain having an average pulse rate 3 KHz can be created at bothelectrodes E1 and E4. As another example, as illustrated in FIG. 12, anelectrical pulse train having a pulse rate of 1 KHz can be conveyed fromelectrode E2 to electrode E1, and an electrical pulse train having apulse rate of 2 KHz can be conveyed from electrodes E3 and E4 toelectrodes E1. It should further be appreciated that although theelectrical pulse trains are bipolar in nature in that they are conveyedbetween two lead electrodes, any of the electrical pulse trains may bemonopolar in nature by conveying the electrical pulse train to or fromthe case electrode.

Although the electrical pulse trains illustrated in FIGS. 6-12 have beendescribed as having the same pulse amplitude, pulse duration, and pulseshape, the electrical pulse trains that are combined into a pulse trainat the common electrode or electrodes may have a different pulseamplitude, pulse duration, and/or pulse shape. For example, asillustrated in FIG. 13, the electrical pulse train conveyed fromelectrode E2 to electrode E1 has a greater amplitude, but smaller pulseduration, then the electrical pulse train conveyed from electrode E3 toelectrode E1. As a result, a combined electrical pulse train having anaverage pulse rate 3 KHz, with varying pulse amplitudes and pulsedurations, can be created at electrode E1.

Furthermore, although the pulses of the electrical pulse trains areillustrated as being rectangular, the pulses can be other shapes,including decaying exponential shaped, increasing exponential shaped,triangularly shaped, sinusoidal shaped, or any combination of shapes.Furthermore, the shape of the pulses may be arbitrarily shaped that canbe programmed. Also, although the illustrated electrical pulse trainsare shown to have uniform pulse shapes, the electrical pulse trains mayhave different pulse shapes within a respective electrical pulse trainor between electrical pulse trains. In an optional embodiment, thepulses of the electrical pulse trains may be created using a number ofsinusoidal cycles.

As will be described in further detail below, the SCM system 10 mayselect the common electrode or electrodes in response to a user entryspecifying such common electrode(s), and then select the electrodes fromwhich the electrical pulse trains are conveyed to the commonelectrode(s) in response to an additional user entry specifying theseelectrodes. Alternatively, the SCM system 10 may automatically selectthe electrodes from which the electrical pulse trains are conveyed tothe common electrode(s) in response to the user entry specifying thecommon electrode(s). For example, this selection can be accomplishedrandomly or in accordance with some set of heuristic rules (e.g.,selecting two or more electrodes closest to the common electrode(s) orfurthest from the common electrode(s)). Optionally, in response to auser entry of electrode(s) that are not desired to be used to conveyelectrical pulse trains, the SCM system 10 may select electrodes that donot include the undesirable electrode.

The SCM system 10 may or may not utilize arbitration when combining theindividual electrical pulse trains into the combined electrical pulsetrain.

If the SCM system 10 does not utilize arbitration, the pulses of eachrespective individual electrical pulse train may be uniformly spacedwhile allowing the pulses of the individual pulse trains to temporallyoverlap each other, as illustrated in FIG. 14. In the case where thereis no arbitration, the maximum time interval between any two pulses inthe combined electrical pulse train will be limited by the highest pulserate of the individual electrical pulse trains, whereas the minimum timeinterval between any two pulses in the combined electrical pulse trainwill be as zero (overlapping pulses edge to edge). Notably, if thegreatest common divisor of the periods of the individual electricalpulse trains is equal to or greater than the sum of the pulse durationsof the individual electrical pulse trains, the pulses of the electricalpulse trains can be interleaved in a manner that will preserve theuniform spacing between the pulses of each electrical pulse train willpreventing overlap between the pulses, as described in U.S. patentapplication Ser. No. 12/550,185, entitled “Methods to Avoid FrequencyLocking in a Multi-Channel Neurostimulation System Using a GreatestCommon Divisor Rule,” which is expressly incorporated herein byreference.

If the SCM system 10 utilizes arbitration, the pulses of at least one ofthe electrical pulse trains are variably spaced from each other in amanner that limits the time intervals between the pulses of the combinedelectrical pulse train to a minimum time interval, which can be as smallas zero.

For example, as illustrated in FIG. 15, a pulse of one of the individualpulse trains that will potentially overlap temporally (or otherwiseviolate the minimum time interval) with a pulse of another of theindividual pulse train (as shown in phantom) may be dropped or cancelledto prevent such overlap or minimum time interval violation. Furtherdetails discussing this technique are described in U.S. patentapplication Ser. No. 12/550,237, entitled “Method to Avoid FrequencyLocking in a Multi-Channel Neurostimulation System Using PulsePlacement,” which is expressly incorporated herein by reference.

In another example, as illustrated in FIG. 16, a pulse of one of theindividual pulse trains that will potentially overlap temporally (orotherwise violate the minimum time interval) with a pulse of another ofthe individual pulse train (as shown in phantom) may be shifted toprevent such overlap or minimum time interval violation. Further detailsdiscussing this technique are described in U.S. patent application Ser.No. 12/550,237, entitled “Method to Avoid Frequency Locking in aMulti-Channel Neurostimulation System Using Pulse Shifting,” which isexpressly incorporated herein by reference.

Notably, the individual electrical pulse train in which a pulse iscancelled or shifted can be selected in accordance with any criteria.For example, a pulse of one individual electrical pulse train thatpotentially overlaps or violates the minimum time interval with a pulseof another individual electrical pulse train that has already occurredmay be selected to be cancelled or shifted. As another example, theindividual electrical pulse trains may be prioritized, such that theindividual electrical pulse train with the lowest priority relative toother electrical pulse trains is selected to have its pulse cancelled orshifted. Such priority may be based on, e.g., the pulse having thelowest pulse amplitude, lowest pulse duration, lowest injected charge,or lowest injected charged density, with the individual electrical pulsetrain having the lowest of these parameters selected to have itspotentially overlapping pulse cancelled or shifted. In otherembodiments, the arbitration rules allow overlap or violation of theminimum time interval between pulses of respective electrical pulsetrains if the summation of the pulses does not exceed a maximum pulseamplitude, maximum pulse duration, maximum injected charge, or maximuminjected charged density.

In the case where the pulses are biphasic, the arbitration rules mayensure that both phases of each biphasic pulse are completed before anyphase of the next biphasic pulse is conveyed. Alternatively, thearbitration rules may allow for the modulation phases for multiplebiphasic pulses to be conveyed before the charge recovery phases ofthese multiple biphasic pulses. For example, the arbitration rules mayalso for two or more cathodic phases before any anodic phase occurs. Inone embodiment, the arbitration rules allows for particular phases ofthe biphasic pulses to overlap while preventing the other phases of thebiphasic pulses from overlapping each other. Optionally, there may bearbitration rules for maximum pulse width and maximum amplitude (notonly frequency) can be provided, so that the combined electrical pulsetrain may have a limit to the maximum frequency, maximum pulse width,and/or maximum amplitude that limit charge injection for pulse to amaximum level or average charge injection per second to a given level.

Optionally, the each of the electrical pulse trains may be generated inaccordance with a cyclically varying set of modulation parameters, suchthat the combined electrical pulse train has a cyclically varying set ofmodulation parameters. The electrical pulse trains may also berepeatedly generated in a bursting pattern. For the purposes of thisspecification, cycling refers to sequences of pulses that are executedin a regular fashion, whereas bursting patterns refer to a limitedduration event (such as a bolus or limited duration sequence). Differentphases of cycling can refer to different pulse rates, electrodecombinations, pulse amplitudes, pulse duration, injected charge,injected charge density or even on-off periods of modulation. Thecycling and bursting patterns can be applied to only one individualelectrical pulse trains or all of the electrical pulse trains, and canbe different between the individual electrical pulse trains. The cyclingand bursting patterns may include different frequencies for thedifferent cycle and burst phases. The cycling and bursting pattern canhave a phase with a given frequency and a phase with a differentfrequency. One phase can have a pulse rate of 1 KHz and higher, whileanother phase can have a pulse rate of less than 1 KHz. In one preferredembodiment, the cycling and burst patterns can include phases as shortas 0.5 ms and as large as one week. In an optional embodiment, secondarycycling patterns can be used one on top of the other in any givenindividual electrical pulse train or combination of electrical pulsetrains. For example, the first cycling pattern can create a pattern oftwo phases (each one lasting less than one hour), and the second cyclingpattern may have phases that are longer than the first cycling (forexample, phases of 24 hours).

In another optional embodiment, the modulation parameters in accordancewith which the electrical pulse trains are conveyed may be modifiedbased on the posture or activity of the patient. In one particulartechnique, the individual electrical pulse trains may be combined tocreate a combined electrical pulse train with a relatively high pulserate, which then switches to a relatively low pulse rate (or evenoff-status) when the SCM system 10 detects that the patient is layingdown, or after a programmable time (e.g., 30 minutes), after laying downfor a period of time, thereby reducing the power consumption.

Turning next to FIG. 17, the main internal components of the IPG 14 willnow be described. The IPG 14 includes modulation output circuitry 50configured for generating electrical modulation energy in accordancewith a defined pulsed waveform having a specified pulse amplitude, pulserate, pulse duration, and pulse shape under control of control logic 52over data bus 54. Control of the pulse rate and pulse duration of theelectrical waveform is facilitated by timer logic circuitry 56, whichmay have a suitable resolution, e.g., 10 μs. The electrical modulationenergy generated by the modulation output circuitry 50 is output toelectrical terminals 58 corresponding to electrodes E1-E16.

The modulation output circuitry 50 may either comprise one or moreindependently controlled electrical sources, which take the form ofcurrent sources and/or current sinks, for providing stimulation pulsesof a specified and known amperage to or from the electrodes 26, orvoltage sources and/or voltage sinks for providing stimulation pulses ofa specified and known voltage at the electrodes 26. The current (orvoltage) sources or sinks include constant current (or voltage) sourcesand associated analog switches to generate the electrical pulse trains.

For example, in the illustrated embodiment, the modulation outputcircuitry 50 comprises a plurality m independent current source pairs 60capable of supplying electrical modulation energy to the electricalterminals 58 at a specified and known amperage. One current source 62 ofeach pair 60 functions as a positive (+) or anodic current source, whilethe other current source 64 of each pair 60 functions as a negative (−)or cathodic current source. The outputs of the anodic current source 62and the cathodic current source 64 of each pair 60 are connected to acommon node 66.

In essence, each current source pair 60 takes the form of areconfigurable current source whose polarity can be switched. That is,by activating the anodic current source 62 and deactivating the cathodiccurrent source 64, the current source pair 60 can be configured as ananodic current source, and by deactivating the anodic current source 62and activating the cathodic current source 64, the current source pair60 can be configured as a cathodic current source.

The modulation output circuitry 50 further comprises a low impedanceswitching matrix 68 through which the common node 66 of each currentsource pair 60 is connected to any of the electrical terminals 58, and acapacitor 70 coupled between the common node 66 of each current sourcepair 60 and the switching matrix 68. Thus, as briefly discussed above,the switching matrix 68 can be operated to concurrently convey aplurality of electrical pulse trains respectively from a plurality ofelectrical terminals 58 (and the corresponding electrodes) to a commonelectrical terminal or terminals (and the corresponding electrode(s)),thereby creating a combined electrical pulse rate having an averagepulse rate greater than any of the pulse rates of the individualelectrical pulse trains.

Hence, it is seen that each of the programmable electrical terminals 58can be programmed to have a positive (sourcing current), a negative(sinking current), or off (no current) polarity. Further, the amplitudeof the current pulse being sourced or sunk to or from a given electrodemay be programmed to one of several discrete current levels, e.g.,between 0 to 10 mA in step voltage/current requirements of the IPG 14.Additionally, in one embodiment, the total current output by a group ofelectrical terminals 58 can be up to ±20 mA (distributed among theelectrodes included in the group). Also, the pulse duration of thecurrent pulses is preferably adjustable in convenient increments, e.g.,from 0 to 1 milliseconds (ms) in increments of 10 microseconds (μs).Similarly, the pulse rate is preferably adjustable within acceptablelimits, e.g., from 0 to 5000 pulses per second (pps). Other programmablefeatures can include slow start/end ramping, burst stimulation cycling(on for X time, off for Y time), interphase (i.e., the duration betweenfirst and second phases of biphasic energy), and open or closed loopsensing modes. Moreover, it is seen that each of the electricalterminals 58 can operate in a multipolar mode, e.g., where two or moreelectrical terminals are grouped to source/sink current at the sametime. Alternatively, each of the electrical terminals 58 can operate ina monopolar mode where, e.g., the electrical terminals 58 are configuredas cathodes (negative), and case of the IPG 14 is configured as an anode(positive).

It can be appreciated that an electrical terminal 58 may be assigned anamplitude and included with any of up to k possible groups, where k isan integer corresponding to the number of channels, and in oneembodiment, is equal to 4, and with each channel k having a definedpulse amplitude, pulse duration, pulse rate, and pulse shape. Otherchannels may be realized in a similar manner. Thus, each channelidentifies which electrical terminals 58 (and thus electrodes) areselected to synchronously source or sink current, the pulse amplitude ateach of these electrical terminals, and the pulse duration, pulse rate,and pulse shape. The individual electrical pulse trains that areconcurrently generated to create the combined electrical pulse train canbe respectively conveyed in the k number of channels. Amplitudes andpolarities of electrodes on a channel may vary, e.g., as controlled bythe RC 16. External programming software in the CP 18 is typically usedto set modulation parameters including electrode polarity, amplitude,pulse rate and pulse duration for the electrodes of a given channel,among other possible programmable features.

The operation of this output stimulation circuitry, includingalternative embodiments of suitable output circuitry for performing thesame function of generating stimulation pulses of a prescribed amplitudeand width, is described more fully in U.S. Pat. Nos. 6,516,227 and6,993,384, which are expressly incorporated herein by reference.

The IPG 14 further comprises monitoring circuitry 72 for monitoring thestatus of various nodes or other points 74 throughout the IPG 14, e.g.,power supply voltages, temperature, battery voltage, and the like.Notably, the electrodes 26 fit snugly within the epidural space of thespinal column, and because the tissue is conductive, electricalmeasurements can be taken between the electrodes 26. Thus, themonitoring circuitry 72 is configured for taking such electricalmeasurements (e.g., current output magnitude, electrode impedance, fieldpotential, evoked action potentials, etc.) for performing such functionsas detecting fault conditions between the electrodes 26 and themodulation output circuitry 50, determining the coupling efficiencybetween the electrodes 26 and the tissue, facilitating lead migrationdetection, etc. In the case where voltage sources (instead of currentsources) are used, the monitoring circuitry 72 can measure theimpedances on the electrodes 26 in order to maintain a desired currentdistribution on the active electrodes 26 by adjusting the voltages onthe active electrodes 26. Furthermore, whether current sources orvoltage sources are used, the monitoring circuitry 72 will be used tomeasure impedances for ensuring that the actual current values bestmatch the desired current values on the electrodes, as will be discussedin further detail below.

The IPG 14 further comprises processing circuitry in the form of amicrocontroller (μC) 76 that controls the control logic over data bus78, and obtains status data from the monitoring circuitry 72 via databus 80. The IPG 14 additionally controls the timer logic 56 andswitching matrix 68. The IPG 14 further comprises memory 82 andoscillator and clock circuitry 84 coupled to the microcontroller 76. Themicrocontroller 76, in combination with the memory 82 and oscillator andclock circuit 84, thus comprise a microprocessor system that carries outa program function in accordance with a suitable program stored in thememory 82. Alternatively, for some applications, the function providedby the microprocessor system may be carried out by a suitable statemachine.

Thus, the microcontroller 76 generates the necessary control and statussignals, which allow the microcontroller 76 to control the operation ofthe IPG 14 in accordance with a selected operating program andmodulation parameters. In controlling the operation of the IPG 14, themicrocontroller 76 is able to individually generate the individualelectrical pulse trains at the electrodes 26 using the modulation outputcircuitry 50, in combination with the control logic 52 and timer logic56, thereby activating selected ones of the electrodes 26, including themonopolar case electrode. In accordance with modulation parametersstored within the memory 82, the microcontroller 76 may control thepolarity, amplitude, rate, pulse duration and channel through which thecurrent modulation pulses are provided. The microcontroller 76 alsofacilitates the storage of electrical parameter data (or other parameterdata) measured by the monitoring circuitry 72 within memory 82, and alsoprovides any computational capability needed to analyze the rawelectrical parameter data obtained from the monitoring circuitry 72 andcompute numerical values from such raw electrical parameter data.

The IPG 14 further comprises an alternating current (AC) receiving coil86 for receiving programming data (e.g., the operating program and/ormodulation parameters) from the RC 16 and/or CP 18 (shown in FIG. 5) inan appropriate modulated carrier signal, and charging and forwardtelemetry circuitry 88 for demodulating the carrier signal it receivesthrough the AC receiving coil 86 to recover the programming data, whichprogramming data is then stored within the memory 82, or within othermemory elements (not shown) distributed throughout the IPG 14.

The IPG 14 further comprises back telemetry circuitry 90 and analternating current (AC) transmission coil 92 for sending informationaldata sensed through the monitoring circuitry 72 to the RC 16 and/or CP18. The back telemetry features of the IPG 14 also allow its status tobe checked. For example, when the RC 16 and/or CP 18 initiates aprogramming session with the IPG 14, the capacity of the battery istelemetered, so that the external programmer can calculate the estimatedtime to recharge. Any changes made to the current stimulus parametersare confirmed through back telemetry, thereby assuring that such changeshave been correctly received and implemented within the implant system.Moreover, upon interrogation by the RC 16 and/or CP 18, all programmablesettings stored within the IPG 14 may be uploaded to the RC 16 and/or CP18. The back telemetry features allow raw or processed electricalparameter data (or other parameter data) previously stored in the memory82 to be downloaded from the IPG 14 to the RC 16 and/or CP 18.

The IPG 14 further comprises a rechargeable power source 94 and powercircuits 96 for providing the operating power to the IPG 14. Therechargeable power source 94 may, e.g., comprise a lithium-ion orlithium-ion polymer battery.

The rechargeable battery 94 provides an unregulated voltage to the powercircuits 96. The power circuits 96, in turn, generate the variousvoltages 98, some of which are regulated and some of which are not, asneeded by the various circuits located within the IPG 14. Therechargeable power source 94 is recharged using rectified AC power (orDC power converted from AC power through other means, e.g., efficientAC-to-DC converter circuits, also known as “inverter circuits”) receivedby the AC receiving coil 86. To recharge the power source 94, theexternal charger 22 (shown in FIG. 1), which generates the AC magneticfield, is placed against, or otherwise adjacent, to the patient's skinover the implanted IPG 14. The AC magnetic field emitted by the externalcharger induces AC currents in the AC receiving coil 86. The chargingand forward telemetry circuitry 88 rectifies the AC current to produceDC current, which is used to charge the power source 94. While the ACreceiving coil 86 is described as being used for both wirelesslyreceiving communications (e.g., programming and control data) andcharging energy from the external device, it should be appreciated thatthe AC receiving coil 86 can be arranged as a dedicated charging coil,while another coil can be used for bi-directional telemetry.

It should be noted that the diagram of FIG. 17 is functional only, andis not intended to be limiting. Those of skill in the art, given thedescriptions presented herein, should be able to readily fashionnumerous types of IPG circuits, or equivalent circuits, that carry outthe functions indicated and described, which functions include not onlyproducing a stimulus current or voltage on selected groups ofelectrodes, but also the ability to measure electrical parameter data atan activated or non-activated electrode.

Additional details concerning the above-described and other IPGs may befound in U.S. Pat. No. 6,516,227, U.S. Patent Publication No.2003/0139781, and U.S. patent application Ser. No. 11/138,632, entitled“Low Power Loss Current Digital-to-Analog Converter Used in anImplantable Pulse Source,” which are expressly incorporated herein byreference. It should be noted that rather than an IPG, the SCM system 10may alternatively utilize an implantable receiver-stimulator (not shown)connected to leads 12. In this case, the power source, e.g., a battery,for powering the implanted receiver, as well as control circuitry tocommand the receiver-stimulator, will be contained in an externalcontroller inductively coupled to the receiver-stimulator via anelectromagnetic link. Data/power signals are transcutaneously coupledfrom a cable-connected transmission coil placed over the implantedreceiver-stimulator. The implanted receiver-stimulator receives thesignal and generates the stimulation in accordance with the controlsignals.

As briefly discussed above, the IPG 14 may be programmed to control theconveyed electrical energy in accordance with the set of modulationparameters. More significant to the present inventions, the RC 16 and/orCP 18 may include a user interface in which user commands are input tospecify the electrode or electrodes from which high frequency electricalenergy will be delivered.

In particular, in one embodiment, the user interface receives an inputfrom a user specifying the common electrode or electrodes 26 (andcorresponding common electrical terminal or terminals 58) to which theindividual electrical pulse trains is conveyed to create the highfrequency electrical energy at the common electrode or electrodes 26,and control circuitry (which may be the microcontroller 76 or thecontroller in the RC 16 and/or CP 18) may select the common electrode orelectrodes 26 in response to this user input. The control circuitry mayalso automatically select the electrodes 26 from which the individualelectrical pulse trains are conveyed in response to this user input.

Alternatively, user commands specifying the electrodes from which theindividual electrical pulse trains are conveyed can be entered into theuser interface, and the control circuitry may select these electrodes 26to convey these individual electrical pulse trains in response to thisuser input. Optionally, user commands specifying the electrodes fromwhich the individual electrical pulse trains are not be conveyed can beentered into the user interface, and the control circuitry may selectelectrodes 26, which do not include the user specified electrodes, fromwhich the individual electrical pulse trains are conveyed in response tothis user input.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

1. (canceled)
 2. A method comprising: treating chronic pain withoutcausing paresthesia using a plurality of electrodes, the plurality ofelectrodes including a common electrode adjacent to spinal cord tissueto be therapeutically modulated to treat chronic pain and furtherincluding at least two electrodes different than the common electrode,wherein treating chronic pain without causing paresthesia includesdelivering a combined electrical waveform, including concurrentlydelivering at least two waveforms from the at least two electrodes,respectively, to the common electrode to provide the combined waveformfrom the common electrode to the volume of tissue to treat the chronicpain without causing paresthesia.
 3. The method of claim 2, whereindelivering the combined electrical waveform includes delivering acombined electrical waveform with a frequency equal to or greater than 1KHz and less than 50 KHz to treat chronic pain without causingparesthesia.
 4. The method of claim 2, wherein the combined waveform hasa frequency greater than either of the at least two waveforms.
 5. Themethod of claim 4, wherein the combined waveform includes pulses, andthe frequency of the combined waveform includes a pulse rate.
 6. Themethod of claim 2, wherein the combined electrical waveform at thecommon electrical terminal is anodic.
 7. The method of claim 2, whereinthe at least two electrical waveforms have pulse rates, and the combinedelectrical waveform has an average pulse rate equal to a sum of thepulse rates for the at least two electrical waveforms.
 8. The method ofclaim 2, wherein the at least two electrical waveforms are generatedusing a single electrical source.
 9. The method of claim 2, wherein theat least two electrical waveforms are generated using a plurality ofelectrical sources.
 10. The method of claim 2, further comprising usinga user interface to receive a user input identifying the commonelectrode.
 11. The method of claim 10, wherein further comprisingautomatically selecting the at least two electrodes in response to theuser input identifying the common electrode.
 12. The method of claim 10,further comprising using the user interface to receive a user inputidentifying the at least two electrodes different than the commonelectrode.
 13. The method of claim 10, further comprising using the userinterface to receive a user input identifying an electrode to beexcluded when selecting the at least two electrodes.
 14. The method ofclaim 2, wherein the at least two electrical waveforms have differentamplitudes.
 15. The method of claim 2, wherein the at least twoelectrical waveforms have different shapes.
 16. The method of claim 2,wherein the at least two waveforms are multiphasic.
 17. The method ofclaim 2, further comprising generating each of the at least twowaveforms in accordance with a cyclically varying set of modulationparameters.
 18. A method, comprising: treating chronic pain withoutcausing paresthesia using a plurality of electrodes, the plurality ofelectrodes including both a first common electrode and a second commonelectrode adjacent to spinal cord tissue to be therapeutically modulatedto treat chronic pain and further including a first group of at leasttwo electrodes different than the first common electrode and a secondgroup of at least two electrodes different than the second commonelectrode, wherein treating chronic pain without causing paresthesiaincludes delivering both a first combined electrical waveform and asecond combined electrical waveform, including concurrently deliveringat least two electrical waveforms from the first group of at least twoelectrodes to the first common electrode to provide the first combinedelectrical pulse train from the first common electrode to the volume ofspinal cord tissue, wherein delivering the second combined electricalwaveform includes delivering at least two electrical waveforms from thesecond group of at least two of electrodes to the second commonelectrode to provide the second combined electrical waveform from thesecond common electrode to the volume of spinal cord tissue.
 19. Themethod of claim 18, wherein the first and second combined electricalwaveforms block or otherwise disrupt naturally occurring actionpotentials within neural fibers to treat chronic pain without causingparesthesia.
 20. The method of claim 19, wherein delivering the combinedelectrical waveform includes delivering a combined electrical waveformwith a frequency equal to or greater than 1 KHz and less than 50 KHz totreat chronic pain without causing paresthesia.
 21. The method of claim20, wherein the at least two electrical waveforms have different shapes.